The invention relates generally to a container formed of a non-electrically-conducting substrate having an electrically-conductive component so that the container has an RF shield to attenuate RF energy in the container from leaking out of the container, and more particularly, to an RF shield that includes a tortuous path seal.
As a general summary, in the field of medication administration containers are used to store medications before administration to a patient. In RFID tracking systems of today, the medications include an attached RFID tag that responds to RFID interrogation energy. When taking an inventory of a container in which RFID-tagged medications are stored, it is important that the RF activation energy transmitted by an RFID reader to the container stay within the container. Otherwise, medications that have RFID tags located outside the container may be activated by the transmitted RF energy and are read by the RFID reader. The results would therefore be inaccurate for an inventory of the container because the reader would record that the medications outside the container are inside the container when they actually are not. Shielding the container so that RF energy transmitted into the container is attenuated by the container's RF shield that it cannot activate an RFID tag outside the container is desired to avoid this problem.
Medication dispensing systems have been in use for many years. The initial purpose of such systems was to reduce medication errors associated with manual distribution and the high cost of maintaining a large amount of inventory. Current systems present many advantages, including lower costs associated with pharmaceutical distribution, improved inventory control, substance control, automated documentation, further reduction of errors, and relieving professional pharmacists and nursing personnel of many tasks.
In large medical facilities, the main inventories of pharmaceutical items are held in storage locations which are often far removed from the patients who use them. To facilitate secure and accurate delivery of the pharmaceutical items from these storage locations to the patient, a variety of systems have been proposed and put into use. In earlier systems referred to as “cart exchange” systems, medication carts are distributed at nursing stations in the medical facility, remote from the central pharmacy, and are periodically exchanged with fully supplied carts. Typically, these carts contain a twenty-four hour supply of medications sorted by patient into specific drawers. The “used” cart is returned to a central pharmacy supply area where the next twenty-four hours of medications are replenished. Narcotics are stored in locked boxes on the floor, requiring two nurses with separate keys and a written log.
Radio-frequency identification (“RFID”) is the use of electromagnetic energy (“EM energy”) to stimulate a responsive device known as an RFID “tag” or transponder to identify itself and in some cases, provide additionally stored data. RFID tags typically include a semiconductor device having a memory, circuitry, and one or more conductive traces that form an antenna. Typically, RFID tags act as transponders, providing information stored in the semiconductor device memory in response to an RF interrogation signal received from a reader, also referred to as an interrogator.
RFID tags may be incorporated into or attached to articles to be tracked. In some cases, the tag may be attached to the outside of an article with adhesive, tape, or other means and in other cases, the tag may be inserted within the article, such as being included in the packaging, located within the container of the article, or sewn into a garment. The RFID tags are manufactured with a unique identification number which is typically a simple serial number of a few bytes with a check digit attached. This identification number is incorporated into the tag during manufacture. The user cannot alter this serial/identification number and manufacturers guarantee that each serial number is used only once. This configuration represents the low cost end of the technology in that the RFID tag is read-only and it responds to an interrogation signal only with its identification number. Typically, the tag continuously responds with its identification number. Data transmission to the tag is not possible. These tags are very low cost and are produced in enormous quantities.
Such read-only RFID tags typically are permanently attached to an article to be tracked and, once attached, the serial number of the tag is associated with its host article in a computer data base. For example, a particular type of medicine may be contained in hundreds or thousands of small vials. Upon manufacture, or receipt of the vials at a health care institution, an RFID tag is attached to each vial. Each vial with its permanently attached RFID tag will be checked into the data base of the health care institution upon receipt. The RFID identification number is associated in the data base with the type of medicine, size of the dose in the vial, and perhaps other information such as the expiration date of the medicine. Thereafter, when the RFID tag of a vial is interrogated and its identification number read, a processor will compare the identification number to the data base of the health care institution to match that identification number with its stored data about the contents of the vial. The contents of the vial can then be determined as well as any other characteristics that have been stored in the data base. In this system, the institution maintains a comprehensive data base regarding the articles in inventory rather than incorporating such data into each RFID tag separately.
An object of the RFID tag is to associate it with an article throughout the article's life in a particular facility, such as a manufacturing facility, a transport vehicle, a health care facility, a storage area, or other, so that the article may be located, identified, and tracked, as it is moved. For example, knowing where certain medical articles reside at all times in a health care facility can greatly facilitate locating needed medical supplies when emergencies arise. Similarly, tracking the articles through the facility can assist in generating more efficient dispensing and inventory control systems as well as improving work flow in a facility. Additionally, expiration dates can be monitored electronically and those articles that are older and about to expire can be moved to the front of the line for immediate dispensing. This results in better inventory control and lowered costs.
Other RFID tags are writable and information about the article to which the RFID tag is attached can be programmed into the individual tag. While this can provide a distinct advantage when a facility's computer servers are unavailable, such tags cost more, depending on the size of the memory in the tag. Programming each one of the tags with information contained in the article to which they are attached involves further time and expense.
RFID tags may be applied to containers or articles to be tracked by the manufacturer, the receiving party, or others. In some cases where a manufacturer applies the tags to the product, the manufacturer will also supply a respective data base file that links the identification number of each of the tags to the contents of each respective article. That manufacturer supplied data base can be distributed to the customer in the form of a file that may easily be imported into the customer's overall data base thereby saving the customer from the expense of creating the data base.
Many RFID tags used today are passive in that they do not have a battery or other autonomous power supply and instead, must rely on the interrogating energy provided by an RFID reader to provide power to activate the tag. Passive RFID tags require an electromagnetic field of energy of a certain frequency range and certain minimum intensity in order to achieve activation of the tag and transmission of its stored data. Another choice is an active RFID tag; however, such tags require an accompanying battery to provide power to activate the tag, thus increasing the expense of the tag and making them undesirable for use in a large number of applications.
Depending on the requirements of the RFID tag application, such as the physical size of the articles to be identified, their location, and the ability to reach them easily, tags may need to be read from a short distance or a long distance by an RFID reader. Such distances may vary from a few centimeters to ten or more meters. Additionally, in the U.S. and in other countries, the frequency range within which such tags are permitted to operate is limited. As an example, lower frequency bands, such as 125 KHz and 13.56 MHz, may be used for RFID tags in some applications. At this frequency range, the electromagnetic energy is less affected by liquids and other dielectric materials, but suffers from the limitation of a short interrogating distance. At higher frequency bands where RFID use is permitted, such as 915 MHz and 2.4 GHz, the RFID tags can be interrogated at longer distances, but they de-tune more rapidly as the material to which the tag is attached varies. It has also been found that at these higher frequencies, closely spaced RFID tags will de-tune each other as the spacing between tags is decreased.
There are a number of common situations where the RFID tags may be located inside enclosures. Some of these enclosures may have entirely or partially metal or metallized surfaces. Examples of enclosures include metal enclosures (e.g., shipping containers), partial metal enclosures (e.g., vehicles such as airplanes, buses, trains, and ships that have a housing made from a combination of metal and other materials), and non-metal enclosures (e.g., warehouses and buildings made of wood). Examples of objects with RFID tags that may be located in these enclosures include loose articles, packaged articles, parcels inside warehouses, inventory items inside buildings, various goods inside retail stores, and various portable items (e.g., passenger identification cards and tickets, baggage, cargo, individual life-saving equipment such as life jackets and masks) inside vehicles, etc.
The read range (i.e., the range of the interrogation and/or response signals) of RFID tags is limited. For example, some types of passive RFID tags have a maximum range of about twelve meters, which may be attained only in ideal free space conditions with favorable antenna orientation. In a more realistic situation, the observed RFID tag range is often six meters or less. Therefore, some of the enclosures described above may have dimensions that far exceed the read range of an individual RFID tag. Unless the RFID reader can be placed in close proximity to a target RFID tag in such an enclosure, the tag will not be activated and read. Additionally, metal surfaces of the enclosures present a serious obstacle for the RF signals that need to be exchanged between RFID readers and RFID tags, making RFID tags located behind those metal surfaces difficult or impossible to detect.
In addition to the above, the detection range of the RFID systems is typically limited by signal strength to short ranges, frequently less than about thirty centimeters for 13.56 MHz systems. Therefore, portable reader units may need to be moved past a group of tagged items in order to detect all the tagged items, particularly where the tagged items are stored in a space significantly greater than the detection range of a stationary or fixed single reader antenna. Alternately, a large reader antenna with sufficient power and range to detect a larger number of tagged items may be used. However, such an antenna may be unwieldy and may increase the range of the radiated power beyond allowable limits. Furthermore, these reader antennae are often located in stores or other locations where space is at a premium and it is expensive and inconvenient to use such large reader antennae. In another possible solution, multiple small antennae may be used but such a configuration may be awkward to set up when space is at a premium and when wiring is preferred or required to be hidden.
In the case of medical supplies and devices, it is desirable to develop accurate tracking, inventory control systems, and dispensing systems so that RFID tagged devices and articles may be located quickly should the need arise, and may be identified for other purposes, such as expiration dates. In the case of medical supply or dispensing cabinets used in a health care facility, a large number of medical devices and articles are located closely together, such as in a plurality of drawers. Cabinets such as these are typically made of metal, which can make the use of an external RFID system for identification of the stored articles difficult. In some cases, such cabinets are locked due to the presence of narcotics or other medical articles or apparatus within them that are subject to a high theft rate. Thus, manual identification of the cabinet contents is difficult due to the need to control access.
Providing an internal RFID system in such a cabinet can pose challenges. Where internal articles can have random placement within the cabinet, the RFID system must be such that there are no “dead zones” that the RFID system is unable to reach. In general, dead zones are areas in which the level of coupling between an RFID reader antenna and an RFID tag is not adequate for the system to perform a successful read of the tag. The existence of such dead zones may be caused by orientations in which the tag and the reader antennae are in orthogonal planes. Thus, articles placed in dead zones may not be detected thereby resulting in inaccurate tracking of tagged articles.
Often in the medical field, there is a need to read a large number of tags attached to articles in such an enclosure, and as mentioned above, such enclosures have limited access due to security reasons. The physical dimension of the enclosure may need to vary to accommodate a large number of articles or articles of different sizes and shapes. In order to obtain an accurate identification and count of such closely-located medical articles or devices, a robust electromagnetic energy field must be provided at the appropriate frequency within the enclosure to surround all such stored articles and devices to be sure that their tags are all activated and read. Such medical devices may have the RFID tags attached to the outside of their containers and may be stored in various orientations with the RFID tag (and associated antenna) pointed upwards, sideways, downward, or at some other angle in a random pattern.
It is a goal of many health care facilities to keep the use of EM energy to a minimum, or at least contained. The use of high-power readers to locate and extract data from RFID tags is generally undesirable in health care facilities, although it may be acceptable in warehouses that are sparsely populated with workers, or in aircraft cargo holds. Radiating a broad beam of EM energy at a large area, where that EM energy may stray into adjacent, more sensitive areas, is undesirable. Efficiency in operating a reader to obtain the needed identification information from tags is an objective. In many cases where RFID tags are read, hand-held readers are used. Such readers transmit a relatively wide beam of energy to reach all RFID tags in a particular location. While the end result of activating each tag and reading it may be accomplished, the transmission of the energy is not controlled except by the aim of the user. Additionally, this is a manual system that will require the services of one or more individuals, which can also be undesirable in facilities where staff is limited. In many such systems, the RFID reader is a portable unit with a “tethered reader head” thereby imposing the extra time and effort to find the unit, be sure it is powered, take it to the medication cabinet where the inventory is required, open the cabinet, collect the inventory data, and then upload the inventory data to a pharmacy server. All of the foregoing can take significant amounts of time.
A problem often arises where only the RFID tags attached to medical articles located in a particular location or container are to be read for inventory purposes. For example, a tray of medical articles may exist with each of the articles in the tray having an attached RFID tag. Where the articles in the tray must be checked for possible expiration, it is common to activate the RFID tags in the tray by directing an RFID reader's beam at the tray. This will activate the RFID tag on each of the medical articles in the tray. The activated RFID tags will transmit their individual identification numbers which are received by the RFID reader. Those received identifications are communicated from the RFID reader to a processor that accesses a database to compare each received identification number to a medical article in the database to determine if any are expired.
While this system works well, problems arise when the activating RFID beam was strong enough to reach the RFID tags on medical articles that are stored in the locality of the tray but are not in the tray. The tags of these remote articles will also be activated, they will transmit their identification data, and the RFID reader will read their identifications, not knowing that those medical articles are not in the tray. If one of those medical articles having an activated tag that is located outside the tray is determined to be expired, inaccuracy and time wasting can result. Even though the tray itself does not have any expired articles in it, it will probably be removed from use because the reading process identified an expired article. Then each medical article in the tray will now likely need to be visually inspected to determine if it is expired. The item that was reported expired will not be found in the tray but the tray is unavailable for use until this discrepancy has been found.
Consequently, manufacturers of RFID tracking systems strive to furnish an electrical isolation container also called an RF shielded container, within which the tray is placed before it is scanned. The RF shielded container is sometimes referred to as a Faraday cage and its six metallic and electrically connected walls greatly attenuate the passage of electrical energy into and out of the container. The RFID reader antenna(s) is placed inside the RF shielded container. However, the radiated signal will leak out of gaps, slots, openings, and other discontinuities that may be present in the RF shielded container. These leaked signals are free to radiate in open space and may cause the activation of remote RFID tags. Conversely, signals can travel into the RF shielded container in the same manner.
For RFID reading energy having higher frequencies, good shielding effectiveness can usually be achieved by the use of thin metal shielding as the container material or lining, but the assumption is that the shield is continuous and fully surrounds the RFID-tagged articles without gaps or apertures. However, it has been found that gaps or apertures and other openings can be very difficult to avoid. Seams needed for manufacturing, doors, drawers, and other openings made for various purposes penetrate the shielded container, which can lower the shielding performance of the container. Welding, brazing, or soldering is used to make seams between sheets that are permanently secured. The metal faces to be joined must be clean to promote complete filling of the seam with conductive metal. Screws or rivets are less satisfactory methods to secure the seams because permanent low-impedance contact along the seams between the fasteners is difficult to maintain with these methods. A total lack of contact along any part of the seam results in a thin gap capable of acting as a slot antenna. Such an antenna transmits energy at wavelengths shorter than about four times the gap length.
Radio frequency (“RF”) activation energy transmitted within the walls of a Faraday cage container is greatly attenuate at the walls and very little if any energy will leak from that container. As a result only the RFID tags in the isolation container are read. This can then solve the problem of inadvertently reading remote RFID tags that are not in the container; however, making and distributing RF shielded containers have associated problems, some of which have been described above.
In medical applications, current systems used for tracking items with RFID technology consist of heavy, sometimes custom made, and more expensive, metal containers. These metal containers are basic in design due to the cost and difficulty of shaping metal into aesthetically pleasing shapes. These containers consist of sheet metal that has been bent into shape and then welded to form an enclosure. The enclosures are fabricated by hand and therefore are expensive. The sheet metal enclosures are also relatively heavy and therefore require expensive hardware for stacking multiple units or to mount under cabinets, desks, and work stations. The design of the enclosures is that of a basic six-sided enclosure and even when painted appear simple and plain with no design features. In addition, the thermal conductivity of the metal is high compared to plastic or other electrically non-conductive materials making it difficult to insulate these enclosures for cold storage applications.
When such metal enclosures include a drawer or multiple drawers, the weight of the enclosure is even higher. Heavy metal administration or storage cabinets can be difficult to move and place in desired positions and present an even more difficult handling situation when they are required to be stacked on one another.
RFID tracking containers are needed for various storage uses and the sizes required of the containers for such uses are different. A requirement to manufacture different sizes of RFID tracking containers, one for each possible use, can be very expensive and inefficient. Similarly, having to use a shielded container that is much too large for the particular application at hand is inefficient and can be expensive. It would be preferred if a modular approach to assembling an RF shielded container were available. In such a modular approach, various modules of different sizes and configurations would be available, all of which may physically fit together in various configurations as needed, and the RF shielding arrangements of these modules would be designed to fit together to result in a fully RF shielded container for operating an RF tracking system within the container.
Hence, those of skill in the art have recognized a need for modular RF-shielded containers that may be assembled together to form various container shapes and sizes thereby obviating the expense of creating custom containers. Another need has been recognized by those of skill in the art for reducing the cost of medical item containers and reducing their weight. Yet a further need has been recognized for using a less expensive material to build such containers, yet providing such containers so that they nevertheless are RF shielded. Those of skill in the art have also recognized a need for a more reliable configuration of the walls of a container so that when assembled to provide the container, a better RF shield of the container is produced. The invention fulfills these needs and others.